Any mechanics ppl out there willing to help me on this question (exercise 3d of m1)

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Godmaster
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#1
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i dne questions 2-8 (except part b of 8) i need real help on this question!

A ball is thrown vertically upwards with a speed of 10ms from a point 2m above the ground

a) it wants the length of time for which the ball is 3m or more above the ground
b)and the speed at which it hits the ground

i tried it like 10 times and i got like slightly different to the back of the book. could ne1 tell me how to do this question, i actually dnt the other 'particle 1's' except this 1 HELP (
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matouwah
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(Original post by Godmaster)
i dne questions 2-8 (except part b of 8) i need real help on this question!

A ball is thrown vertically upwards with a speed of 10ms from a point 2m above the ground

a) it wants the length of time for which the ball is 3m or more above the ground
b)and the speed at which it hits the ground

i tried it like 10 times and i got like slightly different to the back of the book. could ne1 tell me how to do this question, i actually dnt the other 'particle 1's' except this 1 HELP (
a)s=ut+1/2 at^2 use that equationa nd substitute...

1 = 10t - 4.9t^2....use quadratic equation....should get 2 times....minus smaller one from bigger one.....

b) use.....v^2=u^2+2as

v^2 = 100 - 19.6 (-2)
and solve for v
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Ralfskini
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(Original post by Godmaster)
i dne questions 2-8 (except part b of 8) i need real help on this question!

A ball is thrown vertically upwards with a speed of 10ms from a point 2m above the ground

a) it wants the length of time for which the ball is 3m or more above the ground
b)and the speed at which it hits the ground

i tried it like 10 times and i got like slightly different to the back of the book. could ne1 tell me how to do this question, i actually dnt the other 'particle 1's' except this 1 HELP (
Work out the total time for the flight of the ball then subtract the time when the ball is below 3m high (this can be found by forming a quadratic using x=ut+1/2at^2). The speed at which the ball lands can be found by finding the height the ball reaches, then calculating the speed it will have after accelarating downwards due to gravity(v^2=u^2 + 2ax).
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Godmaster
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(Original post by matouwah)
a)s=ut+1/2 at^2 use that equationa nd substitute...

1 = 10t - 4.9t^2....use quadratic equation....should get 2 times....minus smaller one from bigger one.....

b) use.....v^2=u^2+2as

v^2 = 100 - 19.6 (-2)
and solve for v
1st 1 i tried but it wants above 3m not 2 grr annoying. 2nd 1 i get 8.97ms but that isnt wot it ses at the bk of the book lol.

thnx for trying
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matouwah
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(Original post by Godmaster)
1st 1 i tried but it wants above 3m not 2 grr annoying. 2nd 1 i get 8.97ms but that isnt wot it ses at the bk of the book lol.

thnx for trying
well if it wants above 3m....the displacement will be 1m as u start 2m above ground...so i'm not sure why it doesnt work.......
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Ralfskini
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(Original post by Godmaster)
1st 1 i tried but it wants above 3m not 2 grr annoying. 2nd 1 i get 8.97ms but that isnt wot it ses at the bk of the book lol.

thnx for trying
Well work it out for above 2m. You can work out how long it is bloew 3m for, by saying:

u=10
x=1 (3-2)
a=-9.81

x=ut+1/2at^2
9.81/2t^2 - 10t + 1 =0

t= (10+/-(100-2(9.81))^1/2)9.81
........
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Phil_C
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No no no don't do that for (b)

use original data, displacement is 2 m to ground so u=-10, v=v, s=3, a=g and t='who cares'

v^2=u^2 + 2as
v^2=100 +4g
v=sqrt(100 + 4g)
v=11.7983...
v=11.8m/s
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Phil_C
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Before you ask, set down as the positive direction so acceleration and displacement are +ve values and the initial velocity, upwards becomes negative.

Wherever possible always use data in question to answer supplimentary parts to a problem. The methods descibed above using maximum heights, time above 3m etc are just inviting careless mistakes and round off errors in subsequent calcs.
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byb3
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#9
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(Original post by Godmaster)
i dne questions 2-8 (except part b of 8) i need real help on this question!

A ball is thrown vertically upwards with a speed of 10ms from a point 2m above the ground

a) it wants the length of time for which the ball is 3m or more above the ground
b)and the speed at which it hits the ground

i tried it like 10 times and i got like slightly different to the back of the book. could ne1 tell me how to do this question, i actually dnt the other 'particle 1's' except this 1 HELP (
are these right?

a) = 1.83s
b) = -11.80ms^-1
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